1. Field of the Invention
This invention relates to electrometallurgical processes, namely electrowinning and electrorefining, in which metals are recovered or refined using industrial-scale electrolysis apparatus. Specifically, this invention relates to an improved anode box design for use in such processes.
2. Description of Related Art
Use of large industrial electrolytic cells for the recovery or refining of metals is well-known and widely practiced, particularly in the mining and metallurgy industry. The design or configuration of large industrial electrolytic cells varies, but they usually comprise a tank containing one or more cathodes positioned in proximity to one or more anodes in a bath of electrolyte. A very common configuration of such apparatus is an elongated tank containing a plurality of vertically-oriented cathode plates alternating with a plurality of anodes.
In the process of recovering metals from the electrolyte, i.e., electrowinning, the electrolyte is a purified solution which contains the recoverable metal and the anodes are insoluble. Each anode in the tank is encased in a sheath or diaphragm of porous media through which the electrolyte moves. When an electrical current in applied, electrolyte moves through the diaphragm causing deposition of the metal species on the cathode with a corresponding decrease in acidity in the fluid within the diaphragm, i.e., in the anolyte, and liberation of a gas. The anode, including the diaphragm, is usually designed to carry the gas away from the anode and to remove anolyte from within the diaphragm to maintain and/or optimize the electrowinning process. Examples of electrowinning cells are disclosed in U.S. Pat. No. 4,201,653 and U.S. Pat. No. 4,288,305.
In electrorefining, a target metal is purified or refined from an anode made of the target metal. Application of electricity to the anode causes the target metal to migrate through the electrolyte to the cathode where it is deposited. In most electrorefining processes, the anode is not encased in a diaphragm. However, the refining of some metals causes a sludge of impurities to form in the bottom of the tank, which can be avoided by placing a diaphragm about the anode.
Anodes used in electrometallurgical processes as previously described typically exist in the form of a flat plate of metal having a bar positioned at one end for hanging the anode in the tank and for providing an electrical bus between the anodes of the tank. U.S. Pat. No. 3,981,353 discloses, for example, a method of producing anode plates for electrowinning processes. U.S. Pat. No. 4,201,653 further discloses a means for separating the diaphragm from the anode plate by providing a spacing device, in recognition of the fact that contact between the diaphragm and anode plate in electrowinning reduces the efficient operation of the process. Other anode designs are disclosed in the prior art in which the anode is not in the form of a plate. Thus, for example, U.S. Pat. No. 5,277,777 describes an anode formed of fork-shaped elements which are maintained in a framework.
The environment of electrometallurgical processing tanks is very harsh on both the cathodes and the anodes. Both the cathodes and anodes can undergo warping as a result of the processing. Further, the cathodes are removed after a processing cycle to remove the metals deposited on the cathode. While the anode, particularly in electrowinning processes, does not need to be withdrawn from the tank as frequently as the cathodes, they nonetheless are subject to contact by the cathodes as the cathodes are being removed, and the anodes can be damaged as a result. Others have recognized the need to protect and isolate the anode plate; however, prior efforts to provide an a protective cover have resulted in the production of devices which are, themselves, subject to degradation from the harsh environment of an electrolytic tank. In particular, anode boxes of the known art are structured from many separate pieces which are bonded together, rendering the device structurally weak and vulnerable to chemical degradation.
It would be advantageous to the art, therefore, to provide a protective member for an anode which is structured to protect and stabilize the anode in both electrowinning and electrorefining processes and to provide isolation from the diaphragm (when used) and adjacent cathodes. It would further be advantageous to provide a protective member for an anode which is structured to resist the damage or degradation which inherently results from exposure to the environment of an electrolyte tank.
In accordance with the present invention, an anode box is provided in which an anode plate is positionable for placement in an electrolytic tank. The anode box is structured to protect and stabilize the anode plate and to isolate the anode from adjacent cathode plates and from the diaphragm, when used. The structure of the present invention is particularly advantageous in that it is unitarily formed, comprising two or three pieces, from materials which render the anode box relatively resistant to chemical and mechanical degradation, thereby providing better protection to the anode plate. The anode box of the present invention may be employed in both electrowinning and electrorefining processes.
The present invention comprises a frame sized to receive an anode plate therein. Specifically, the anode box comprises a frame body having two opposing long sides and a third side joining the two opposing long sides together. The outer-facing or peripheral edges of frame may be preferably shaped to facilitate placement of diaphragm or media bag about the frame body. A continuous, U-shaped slot is formed along the three sides of the body and the open fourth side of the frame thereby provides for insertion of an anode plate into the frame with the peripheral sides of the anode plate being supported by the U-shaped slot. A plurality of spacers extend between the sides of the frame body to isolate the anode plate from contact with an adjacent cathode or a diaphragm. The spacers have inwardly projecting members which contact the anode plate to help center the anode plate within the frame body and to provide a space about the anode plate through which gas liberated in the electrolytic process can escape.
A removable hood structured to span the two opposing long sides is positionable on the frame body to provide a fourth side of the frame body, thereby fully enclosing the anode plate therewithin. The removable hood is structured to support an electrical bus and has a gas release mechanism for releasing chemically-liberated gas from around the anode plate. The removable hood may also be configured with an attachment structure to which a diaphragm, or bag of porous media, may be attached.
The anode box of the present invention is unitarily and integrally formed from materials which are comparatively resistant to chemical and mechanical degradation. For example, the frame body, including the sides and spacers, is formed from polymer materials, such as polypropylene, PVC (polyvinyl chloride) or other materials. A particularly suitable material may, for example, be polypropylene in which is incorporated glass beads. The anode box may preferentially be made by a molding process. The frame body may also be formed by extrusion and then processed by known milling techniques to provide the desired configuration. The anode box of the present invention is, therefore, structurally strong to protect the anode plate and reduce warping of the anode plate, and, because it is unitarily formed, it is not subject to degradation.